Sept. 1, 2010 -- Actor Michael Douglas last night stunned a television audience with the announcement that he has "late stage IV throat cancer."

What is this disease? How is it treated? Based on what he's revealed, what do we know about Douglas's treatment and prognosis?

To answer these and other questions, WebMD spoke with two experts:

Gady Har-El, MD, chairman of the department of otolaryngology-head and neck surgery at New York's Lenox Hill Hospital.

Ted Teknos, MD, co-director of the head and neck disease committee and professor of otolaryngology-head and neck surgery at Ohio State University Comprehensive Cancer Center-James Cancer Hospital, Columbus, Ohio.

What is throat cancer?

Surprisingly, doctors don't use the term "throat cancer." Several different kinds of cancer can involve different parts of the throat and mouth.

Michael Douglas says he has a walnut-sized tumor at the base of his tongue. If that's truly where his cancer started, he likely has oropharyngeal cancer.

Oropharyngeal cancer may involve the base of the tongue, the tonsils and surrounding tissues, the soft palate, or the front and back walls of the throat.

Doctors use the term "insidious" to describe base-of-tongue tumors. That's because there is no pain sensation at the base of the tongue, so the tumors can become quite advanced before symptoms appear.

What causes throat cancer?

Another reason to suspect that Douglas's throat cancer is oropharyngeal cancer is his statement that the cancer probably was caused by smoking and drinking.

"Smoking is a major cause of oropharyngeal cancer," Har-El tells WebMD. "Drinking alcohol, as far as the statistics can tells us, is not as bad by itself. But the combination of drinking and smoking is the worst combination."

Although it may account for Douglas's cancer, it does not account for the sudden rise in oropharyngeal cases that doctors are seeing.

"This is a disease that is increasing really at a dramatic rate, particularly in the male population," Teknos says. "Not that long ago, this only made up about 18% of head and neck cancers. Now it makes up a full third and is increasing at a very rapid rate."

What's causing the rise in cases, Teknos says, is a surge in the number of cases caused not by smoking and drinking but by human papillomavirus -- HPV, the sexually transmitted virus best known as a cause of cervical cancer and genital warts.

Teknos says an Ohio State study recently found that people with more than six lifetime oral sex partners have the greatest oropharyngeal cancer risk. It's not yet clear why some people with HPV get this throat cancer while others do not. But it does appear that decades can elapse between HPV infection and the appearance of cancer.

"The infection may happen in a person's 20s and only manifest as cancer in the 40s," he says. "We are doing a lot of research to try to identify what is different in people who get the cancer. Because many are exposed, but only a few get cancer."

Can throat cancer be cured?

If caught in its early stages, this "throat cancer" can be cured 85% of the time by surgery or radiation.

Later stages are more problematic. Douglas says his doctors have diagnosed "late stage IV" cancer.

"For the advanced stage IV cancers, it depends on the situation with the lymph nodes in the neck," Har-El says. "There is over a 60% chance of remission if it has not spread to the lymph nodes. But if it already has spread to the lymph nodes in the neck, the odds of remission are more like 40% or 30%."

Douglas says his cancer has spread to his head and neck, but that his doctors say his odds of survival are 80%.

Teknos says there's no reason to doubt this assessment.

"We think he is still in the curable category, stage IVa," he says. "Of course we don't know, but his curability could be quite acceptable."

Interestingly, oropharyngeal cancer caused by HPV is much more easily cured -- even at late stages -- than cancer caused by smoking and drinking.

What are the symptoms of throat cancer?

The most common symptoms of oropharyngeal cancer, Har-El says, include:

Throat pain

Difficulty swallowing

Ear pain (which is actually pain from the base of the tongue referred to the ear)

Bleeding in the mouth or throat

Hoarseness

A lump in the throat, or the feeling that something is stuck in the throat

Any of these symptoms may signal throat cancer.

"I want people, especially smokers, who have what appear to be simple, stupid symptoms to see an ear, nose, and throat doctor," Har-El says. "All of us have hoarseness at end of the day, but if it persists over three weeks, see the doctor."

Har-El says that patients with ear pain often go to their doctor, who looks in their ear and tells them nothing is wrong.

"If you go to your doctor with ear pain and he says your ear is fine and unrelated to any other problem, go see an ear, nose, and throat doctor," he says.

What is the treatment for throat cancer? What are the side effects?

Treatment for early stage oropharyngeal cancer has traditionally been radiation, usually along with chemotherapy. But Har-El says surgery is becoming more and more popular, because small throat tumors can be removed with minimally invasive surgery or even with robotic surgery.

"This spares the patient radiation therapy, which is quite taxing to the patient," Har-El says.

Advanced tumors present more of a challenge.

"One is to do very, very big surgery. This removes the base of the tongue but sometimes also the voice box, because the base of the tongue prevents food from going through the voice box into the windpipe," Har-El says.

However, Teknos notes that reconstructive surgery can use tissues from other parts of the body to repair the base of the tongue. This technique makes it unnecessary for the surgeon to remove the voice box.

The other option for late stage oropharyngeal cancer is radiation and chemotherapy, which Douglas began three weeks ago. Surgery would be necessary only if this treatment fails.

While avoiding surgery, the side effects of radiation and chemotherapy are severe.

"The first few weeks are no big problem, but then patients often have significant difficulty with swallowing," Har-El says. "In most cancer centers -- and we certainly do it with advanced base-of-the-tongue tumors -- they insert a feeding tube right into the stomach through the belly. Mostly we try to do it ahead of time, before problems start, because if you do it later you have to interrupt treatment."

Another serious problem is that the radiation can burn the mouth and throat, sometimes raising blisters. And patients usually suffer severe fatigue during treatment.

Although the burns, fatigue, and swallowing problem usually go away after therapy, patients may have another problem for the rest of their lives: dryness of the mouth and throat.

"Radiation kills the tumor, but it also kills the salivary glands in the throat," Har-El says. "That is why, if you go into our waiting room, everybody is carrying a bottle of water all the time."